[CentOS] Comparing directories recursively

Sat Oct 28 16:30:46 UTC 2017
H <agents at meddatainc.com>

On October 28, 2017 8:10:34 AM EDT, Rich <centos at foxengines.net> wrote:
>On Fri, Oct 27, 2017 at 05:27:22PM -0400, H wrote:
>> What is the best tool to compare file hashes in two different
>drives/directories such as after copying a large number of files from
>one drive to another? I used cp -au to copy directories, not rsync,
>since it is between local disks.
>> Are there other tools for this automatic compare where I am really
>looking for a list of files that exist in only one place or where
>checksums do not match?
>rsync obviously offers the 'exist in only one place' feature but also
>offers checksum comparisons (in version 3 and higher, I understand)...
>-c, --checksum
>      This changes the way rsync checks if the files have been changed
>      and  are in need of a transfer.  Without this option, rsync uses
>      a "quick check" that (by default) checks if each file’s size and
>      time of last modification match between the sender and receiver.
>      This option changes this to compare a 128-bit checksum for  each
>      file  that  has a matching size.  Generating the checksums means
>      that both sides will expend a lot of disk I/O  reading  all  the
>      data  in  the  files  in  the transfer (and this is prior to any
>      reading that will be done to transfer changed  files),  so  this
>      can slow things down significantly.
>      The  sending  side generates its checksums while it is doing the
>      file-system scan that builds the list of  the  available  files.
>      The  receiver  generates  its  checksums when it is scanning for
>      changed files, and will checksum any file that has the same size
>      as the corresponding sender’s file:  files with either a changed
>      size or a changed checksum are selected for transfer.
>      Note that rsync always verifies that each transferred  file  was
>      correctly  reconstructed  on  the  receiving  side by checking a
>      whole-file checksum that is generated  as  the  file  is  trans‐
>      ferred,  but  that automatic after-the-transfer verification has
>      nothing to do with this option’s before-the-transfer "Does  this
>      file need to be updated?" check.
>      For  protocol  30  and  beyond  (first  supported in 3.0.0), the
>      checksum used is MD5.  For older protocols, the checksum used is
>      MD4.
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Thank you, this time I used diff.